1910.| Some Enumerative Studies on Malarial Fever. 167 
without fever, and as few as 150 and 50 in Cases 5 and 9 with very slight 
fever (98°°6 F.), so that about 200 to 500 may perhaps be taken as the usual 
limit. With P. faleiparwm, as many as 1620 (asexual) were found as an 
average of four non-febrile days in Case 26, and 1196 as an average of six 
non-febrile days in Case 25; while in Case 18 from 16 to 1860 were present 
for 22 days without causing any marked fever, so that 600 to 1500 may 
perhaps be adopted as the usual limit. With P. malariw (Case 1), an 
average of 79 were present for 13 days without fever, but about 140 twice 
caused slight rigor. 
8. Lhe Asexual Forms between the Relapses.—It is generally thought and 
taught that these forms tend to “disappear” between the relapses—though 
of course exceptions, especially in children, are noted—and to reappear 
during them; and several hypotheses, such as that of parthenogenesis 
(F. Schaudinn), have been advanced to explain the supposed phenomenon, and 
have led to what appears to be much waste of work. We find that the asexual 
forms do not necessarily disappear at all between the relapses, but are generally 
still to be found in small numbers per cubic millimetre on most of the 
days. The apyretic periods preceding the 13 relapses in our cases (7, 17, 18, 
19, 20, 25, 24, 26, 32) lasted 114 days altogether (nearly nine days each on 
the average). On 18 of these days no observations were made; but on the 
remaining 96 days the parasites were found in small numbers on 59, or 61 per 
cent., and were not found only on 37. Moreover, the general trend of the 
curves suggests that they were not found on these days only because their 
numbers were a little too few for detection. The parasite curve, at its 
height during a pyrexial period, generally falls very rapidly at first and more 
slowly later, and tends to reach its lowest about half-way between two 
apyrexial periods. At this point it may or may not remain above the detect- 
able limit (by thick-film methods). After this it was observed (by D. T.), 
especially in Cases 7, 17, 23, and 24, to begin mounting slowly at first, until, 
when it reached the pyrogenic limit, another pyrexial period commenced. All 
this is scarcely compatible with the speculation that the apyrexial periods 
are due to the abrupt death of most of the asexual Plasmodia, or to their con- 
version into “ resting stages,” etc. Nor dosuch speculations appear to be at all 
necessary. It is easy to see that the survival of comparatively small numbers 
of the asexual forms will suffice to keep the infection alive, not only for the 
short periods observed by us, but for “relapses of long interval,’ and for 
months or years. Obviously, if only a few parasites per cubic milli- 
metre are present, they may easily be overlooked in the small amount 
of blood (say 01 cu. mm.) usually examined by thin film, and may 
then be reported as being absent: yet many millions may still exist 
